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Effects of Anoxia Treatment on Tomato Fruit Quality
Wiraya Krongyut1 and Sirichai Kanlayanarat2
Abstract
Tomato (Solanum lycopersicum L.) is one of the most important and widely
cultivated vegetables in the world. Being a fleshy fruit, it continues to lose water after
harvest resulting in shriveling and dull appearance which reduces the eye appeal and
freshness and eventually becomes unmarketable. To extend the storage life of tomatoes,
regulation of ripening by retarding the metabolic activities coupled with prevention of
microbial attack is an important consideration. This study examined the effect of anoxia
(99% N2) treatment for 24 h, 48 h and 72 h on fruit quality which was evaluated in terms
of weight loss, peel colour (Hue angle), firmness, total soluble solids (TSS), physical
damage and sensory quality of green and pink tomatoes subsequently held for two weeks
at 20°C. Results showed that anoxia treatment for 24 h maintained the best physical
quality of the fruit. Anoxia treatment inhibited ripening based on changes in firmness and
physical damage and sensory qualities of green and pink fruits.
Keywords: anoxia, tomato, fruit quality
Introduction
Tomato (Solanum lycopersicum L.) is one of the most important and widely
cultivated vegetables in the world. The tomato fruit contains about 94.5% water per 100 g
of fresh weight, 16% protein per 100 g of dry weight, 71.27% carbohydrate, 21.82% of
total dietary fibre, 15145.45 IU of vitamin A and 230.91 mg of ascorbic acid
(Organisation for Economic Co-operation and Development, 2008).
Consumer’s increasing desire for high quality and nutritious foods has created a
need for longer market season for both domestic as well as export markets (Babitha,
2006). Fresh tomato quality is a function of appearance, colour, texture and flavour.
Optimum quality is attained through vine ripening. But, ripe tomatoes are perishable and
very susceptible to shipping damage which consequently leads to loss of quality and
waste (Nakhasi et al., 1991). Hence, tomatoes are harvested when mature but before
ripening has begun.
Tomato is a climacteric fruit; the start of ripening is accompanied by a rapid rise
in respiration rate during which oxidative breakdown of complex substrates occur,
eventually leading to product deterioration (Babitha, 2006). Also tomatoes being fleshy
fruits, continue to lose water after harvest. This results in shriveled, dull appearance that
reduces the eye appeal and freshness and eventually renders the fruit unmarketable.
To extend the storage life of tomatoes, regulation of ripening by retarding the
metabolic activities coupled with prevention of microbial attack is an important
consideration. Several storage methods are being employed, such as refrigeration and
modification of the atmosphere surrounding the produce. Although, the prevalent method
of preserving fresh tomato is by cooling, storage at low temperatures is precluded by their
susceptibility to chilling injury, which causes pitting, poor or uneven ripening and
increased fungal spoilage (Tomkins, 1963, Ryall and Lipton, 1972). On the other hand,
the use of very low levels of O2 or high levels of CO2 has been tested as a means of
postharvest quality maintenance (Ke and Kader, 1992). However, commodities differ in
their tolerance to reduced O2 and/or elevated CO2. Keeping fruit and vegetables in a very
low oxygen atmosphere (anoxia) may have beneficial effects, such as reduction in
respiration rate, inhibition of ethylene production and action, and reduction of the
incidence of some physiological disorders (Ke and Kader, 1992; Pesis et al., 1994).
Several other researchers have found that pretreatment with anoxia can delay fruit
ripening (Lurie and Pesis, 1992; Pesis and Marinansky, 1993; Burdon et al., 1994). Fallik
et al. (2003) added that a short-term anoxia treatment (for 24 h) significantly reduced rot
development in tomato inoculated with Botrytis cinerea, compared to non-treated fruit.
However, a 48 h anoxia treatment reduced fruit quality, damaged the fruit, and caused off
flavor. Off-flavor development has been attributed to ethanol accumulation (Kelly and
Salviet, 1988). These findings suggest that the efficacy of anoxia treatment depends upon
the length of application and type of produce. This study was conducted to evaluate the
effects of different durations of anoxia treatment on the physical and sensory quality of
green and pink tomatoes.
Materials and Methods
Green and pink tomatoes cv. 1912 of uniform size and colour and without any
defects were harvested from a commercial non-heated plastic house from the central part
of Israel. The calyx was removed from each fruit. The tomatoes were weighed. Fruit
color was obtained using a Minolta Chromameter, total soluble solids (TSS) using a
digital refractometer (Atago, Japan), and firmness using a durometer (firmness gauge,
Shore Brothers, USA).
Fifteen green and pink tomatoes were selected and placed inside three 25 L plastic
containers and treated with 99% N2 for 24 h, 48 h and 72 h. Lime was introduced to the
containers to absorb CO2. Fruits without anoxia treatment served as control. All
treatments were replicated three times. Following each treatment, fruits were removed
from the containers and stored for two weeks at 20°C with 70% RH. Fruit quality during
storage was evaluated in terms of weight loss, colour (Hue angle), firmness, TSS and
taste. Anoxia damage was determined visually and expressed as percentage of the total
number of samples per replicate.
Sensory analysis was performed by 6 untrained panelists. Fruit were cut into six
pieces and placed on dark glass dishes. Flavour was scored on a scale of 1-3, with: 1-bad,
2-good and 3-excellent. Off-flavour was evaluated on a scale of 0-3, with: 0-no offflavour,
1-slight off-flavour, 2-moderate off-flavour and 3-strong off-flavour. At the end of the
sensory analysis, panelists indicated their preferred sample. Results were analysed using
Microsoft Excel
Results and Discussion
Anoxia treatment for 48-72 h significantly increased weight loss of green and pink
tomatoes after two weeks of storage; as 24 h treatment, anoxia had no significant effect
(Table 1). Color changes based on hue values did not differ with treatment and generally
decreased with storage in both green and pink tomatoes (Table 2). However, fruit
firmness significantly varied; for green fruits, all anoxia treatments maintained firmer
fruits than the control while for pink fruits, only the 24 h anoxia treatment resulted in
significantly firmer fruits than the control after 2 weeks of storage (Table 3). In terms of
TSS contents, anoxia had no marked effect on green tomatoes while it significantly
increased that of pink tomatoes particularly when applied for 24-48 h (Table 3). In both
green and pink tomatoes, anoxia treatment for 48-72 h increased physical damage and
off-flavor development, decreased taste scores, and consequently reduced the overall
acceptability in both green and pink tomatoes (Table 4-5). In contrast, anoxia for 24 h
generally resulted in comparable responses as the untreated control, except that the
overall acceptability for green tomatoes was improved.
The results indicate that anoxia for 24 h had no adverse effects on quality of green
and pink tomatoes; it even improved soluble solids content of pink tomatoes. The
treatment appeared to slow ripening by maintaining firmer fruits after two weeks of
storage, although this was not accompanied by a corresponding reduction in the rate of
ripening-associated color changes as found in earlier studies (Lurie and Pesis, 1992; Pesis
and Marinansky, 1993; Burdon et al., 1994). Longer duration of anoxia treatment (e.g. 48
h) could damage the fruit and induce off-flavors as a result of ethanol accumulation
(Fallik et al., 2003; Kelly and Salviet, 1988). This has also been found in the present
study with the use of 48-72 h anoxia.
Table 1 Weight loss (% of initial weight) of anoxia-treated and untreated green and pink
tomatoes after 14 days of storage
Anoxia Treatment
Green fruit
Pink fruit
c
0 (Control)
4.4
5.1b
24 h
4.7bc
5.1b
a
48 h
5.6
6.4a
72 h
5.1ab
4.9b
F-test
**
**
CV (%)
4.73
1.32
Mean separation within columns by LSD (P ≤ 0.05)
Table 2 Colour (Hue angle) of anoxia-treated and untreated green and pink tomatoes
after 14 days of storage
Green fruit
Pink fruit
Anoxia
After 2 weeks
After 2 weeks
Treatment
Before storage
Before storage
storage
storage
0 (Control)
117.0
48.5
61.1
48.9
24 h
118.5
48.7
58.5
49.9
48 h
118.2
48.6
55.5
50.9
72 h
116.7
48.3
57.1
50.5
F-test
NS
NS
CV (%)
0.59
1.57
No significant (NS) differences among treatments were obtained after 2 weeks storage.
Table 3 Firmness and total soluble solid (TSS) of anoxia-treated and untreated green and
pink tomatoes after 14 days of storage
Anoxia
Treatment
Firmness (N)
Green fruit
Pink fruit
c
0 (Control)
34.0
17.3b
b
24 h
41.1
19.0a
48 h
42.3ab
16.3c
a
72 h
42.8
16.3c
F-test
**
**
CV (%)
1.25
0.99
Mean separation within columns by LSD (P ≤ 0.05)
TSS (%)
Green fruit
4.3ab
4.2b
4.4ab
4.5a
**
1.63
Pink fruit
4.0b
4.5a
4.2a
3.7c
**
2.24
Table 4 Physical damage and sensory qualities of anoxia-treated and untreated green
tomatoes after 14 days of storage
Overall
Anoxia treatment
Damage (%)
Taste
Off-flavour
acceptability (%)
0 (Control)
33 c
2.3 a
0.3 b
80 b
d
a
c
24 h
27
2.3
0.0
100 a
48 h
67 a
2.0 b
0.3 b
10 c
b
c
a
72 h
53
1.7
1.3
0d
F-test
**
**
**
**
CV (%)
1.28
2.83
12.37
1.36
Mean separation within columns by LSD (P ≤ 0.05)
Table 5
Physical damage and sensory qualities anoxia-treated and untreated pink
tomatoes after 14 days
Anoxia
Overall
Damage (%)
Taste
Off-flavour
treatment
acceptability (%)
0 (Control)
0
3.2
0.2
100
24 h
13
2.5
0.7
80
48 h
27
2.0
1.3
10
72 h
73
2.3
2.0
0
F-test
**
**
**
**
CV (%)
1.28
2.83
12.37
1.36
Mean separation within columns by LSD (P ≤ 0.05)
Conclusion
A short-term anoxia treatment for 24 h appeared to be promising in maintaining
tomato fruit quality. However, follow-up study is important to confirm the results and
establish a solid recommendation for commercial use.
Acknowledgements
The authors thank Prof. Eli Fallik, Head of the Institute of Technology and
Storage of Agricultural Products, Volcani Agricultural Complex, Bet Dagan, Israel and
all his staff members for all the support during the conduct of the experiment. Sincere
thanks also to MASHAV, Israel Centre for International Cooperation of the Ministry of
Foreign Affairs; Agricultural Research Organization (ARO), Ministry of Agriculture, and
Ms. Sigal Parson and Meir Bazelet of Rural Development, Centre for International
Agricultural Development Cooperation (CINADCO) for the opportunity given to me to
attend the International Research and Development Course on Postharvest Physiology,
Pathology and Handling of Fresh Commodities in Israel.
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